Hydrowax is paraffinic fraction with a boiling point typically in the range of 340 to 560° C. which is obtainable from a hydrocracker. Hydrowax can for instance be used for the production of lubricating base oils and as a feedstock for producing lower olefins. Typically, a hydrowax is obtained by subjecting a refinery distillation fraction to a hydrotreating step and subsequently a hydrocracking step.
In EP 0 697 455 A2, a process is described for producing a hydrowax in which process a blend of a flashed distillate and a hydrodemetallised deasphalted oil is subjected to hydrocracking over a stacked bed of a conventional first stage hydrocracking catalyst (NiMoP on alumina) on top of a dedicated second hydrocracking catalyst (NiW on amorphous silica-alumina). The hydrowax thus obtained can be used as the feedstock for a steam cracker to produce ethylene and propylene or as a feedstock for a dewaxing unit or hydroprocessing unit for producing lubricating base oils.
Generally, a higher conversion in the hydrocracker improves the quality of hydrowax as feedstock for a steam cracker or as feed for a base oil plant. However, a higher conversion also means that the hydrowax yield of the hydrocracker becomes smaller.
A drawback of the known processes to produce hydrowaxes is that a higher conversion reduces substantially the ratio of heavy hydrowax over light hydrowax, which in turn reduces substantially the ratio of heavy lubricating base oils over light lubricating base oils.
At a constant level of conversion, a heavier feed to the hydrocracker will result in a heavier hydrowax. However, in order to maintain the hydrowax quality for a heavier hydrocracker feed its conversion level has to be raised which in turn reduces the the ratio of heavy hydrowax over light hydrowax.
Object of the present invention is to provide a process which at a given feed heaviness and conversion level results in a higher ratio of heavy hydrowax to light hydrowax.